1. Field of the Invention
This invention relates to lubricant additives for coating moving paper and paper board webs. More particularly, the invention provides lecithin based lubricant additive formulations having an alcohol ethoxylate surfactant component having a hydrophilic lipophilic balance (HLB) parameter of less than 10.
2. Background of the Invention
Paper and paper board web material is frequently coated to improve properties such as appearance and printability. The coating process involves applying a coating mixture to the paper as it moves at high speed through a coating apparatus. These coatings are typically composed of: (1) pigments, such as Kaolin clay, titanium dioxide, calcium carbonate or silicates; (2) adhesive binders, such as starches, proteins, styrene butadiene latex, or polyvinyl acetates; and (3) additives, which improve or modify specific properties and characteristics of the coating mixture.
A number of chemical phenomena and physical forces (particularly shear forces) can have a detrimental effect, e.g., destroying the integrity and uniformity of both the coating mixture and the coating as it is applied to the paper sheet. When this occurs, costly problems develop both in the application of the coating and in the finish and quality of the coated paper. These problems are widely known to manufacturers of coated papers.
These problems are greatly magnified as the speed of the web moving through the coating apparatus is increased, causing increased shear forces on the coating mixture being applied. Increased speed causes problems in viscosity control, calcification, streaking, whiskering, and generally poor “runnability” (performance) of the coating. These problems ultimately result in a poor quality coated sheet. Uniformity of the coating mix at these high shear levels is critical.
Typically, lubricant additives, such as calcium stearate dispersions or polyethylene dispersions, have been used as an additive to the coating mixture to improve the performance and uniformity of the coating and the overall integrity of the coating mixture. The main function of a lubricant additive in a coating mixture is to increase the lubricity of the coating. However, many other effects of lubricants are known to the art of coating paper. For example, such characteristics as rheological properties, plasticity, smoothness, coating gloss, anti-dusting and improved printing qualities, can be affected by the use of coating lubricants.
U.S. Pat. No. 4,766,015 recites lubricant formulations having a mixture of lecithin, a fatty acid, an emulsifier and a surfactant. The '015 patent recites formulations in which the surfactant was selected from water soluble nonylphenol ethoxylates (NPEs) having an HLB of greater than 13 or water soluble alcohol ethoxylates having an HLB value of between 11 and 13.
International patent publication WO 01/51706 recite various lubricant formulations based on lecithin in combination with at least one fatty acid and a surfactant selected from anionic or high HLB nonyl phenol ethoxylates (NPEs).
U.S. Pat. No. 5,858,933 recites lubricant formulations having a chemically modified lecithin as a lubricant. Although '933 patent asserts that the chemically modified lecithin, e.g., hydroxylated lecithin, eliminates the need for a fatty acid additive, the increased cost associated with chemical modification results in an economically unfeasible lubricant for paper manufacture.
Thus, it would be desirable to provide new less expensive lecithin based lubricant formulations which provide improved processing during the paper making process and improved finished paper properties.